lockup during probing because of a memory stick

If a USB mass storage device was connected when the computer was
turned on or reset and the device is left connected, then the system
locks up somewhere around the ``acpi0: <A M I OEMXSDT> on
motherboard'' line (not exactly deterministically at that line).
Otherwise (if the device is connected or disconnected just before
FreeBSD started booting, or if the device is nowhere near the computer
for the whole booting process), the system boots fine. I'm using a
-CURRENT kernel.

I don't recall this case happening some time ago. But now, this
happens with and without the NEW_PCIB option. I mention this because
``acpi0: <A M I OEMXSDT> on motherboard'' is shortly followed by
``acpi0: reservation of 0, a0000 (3) failed'', whatever that means.